Problem: $ F = \left[\begin{array}{rrr}2 & 1 & -1 \\ 4 & -2 & 0 \\ -1 & 1 & -2 \\ 4 & 2 & 4\end{array}\right]$ What are the dimensions of matrix $ F$ ?
Solution: The first dimension is the number of rows in the matrix. How many rows does $ F$ have? The second dimension is the number of columns in the matrix. How many columns does $ F$ have? So, $ F$ is a 4 $\times$ 3 matrix.